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Study Guide: Cell Types and Organization

Enduring Understanding

Cells have membranes that maintain distinct internal environments, allowing for specialized functions.

The genetic makeup of populations can evolve over time.

Learning Objectives

Identify membrane-bound structures of eukaryotic cells.

Explain the role of internal membranes in compartmentalizing cellular functions.

Compare prokaryotic and eukaryotic cells in terms of compartmentalization.

Discuss endosymbiotic organelles and their ancestral origins.

Key Concepts

1. Cell Types

Prokaryotic Cells:

Lack a true nucleus.

Generally single-celled.

Have a plasma membrane, cytoplasm, and ribosomes.

Eukaryotic Cells:

Contain a true nucleus and membrane-bound organelles.

Can be single-celled (e.g., yeast) or multicellular (e.g., plants, animals).

Organelles allow for compartmentalization of various metabolic processes.

2. Membrane-Bound Organelles

Nucleus: Contains DNA; controls cellular activities.

Mitochondria: Powerhouse of the cell; site of aerobic respiration.

Chloroplasts: Found in plants; site of photosynthesis.

Endoplasmic Reticulum (ER):

Rough ER: Studded with ribosomes; synthesizes proteins.

Smooth ER: Lacks ribosomes; synthesizes lipids and detoxifies.

Golgi Apparatus: Modifies, sorts, and packages proteins for secretion or use within the cell.

Lysosomes: Contain enzymes for digestion of waste materials and cellular debris.

Vesicles: Transport materials within the cell.

3. Endomembrane System

Comprises the ER, Golgi apparatus, lysosomes, and vesicles.

Functions:

Synthesis and transport of proteins.

Metabolism and detoxification of substances.

Movement of lipids and enzymes.

Endosymbiotic Theory

Definition: Proposes that eukaryotic cells originated from a symbiotic relationship between multiple prokaryotic cells.

Key Points:

Mitochondria and Chloroplasts are believed to be derived from free-living bacteria that were engulfed by ancestral eukaryotic cells.

Over time, these organelles became integral, losing the ability to live independently.

Evidence Supporting Endosymbiosis

Prokaryotic Characteristics:

Both organelles contain circular DNA, similar to that of bacteria.

Their ribosomes are more similar in size to those in prokaryotes than those in the eukaryotic cytoplasm.

Reproduction:

Mitochondria and chloroplasts replicate independently of the cell’s nucleus, through a process akin to binary fission.

Genetic Studies:

DNA analysis reveals that mitochondrial DNA is closely related to certain bacteria (e.g., Rickettsia).

Studies show relationships between eukaryotic host DNA and Archaea, supporting the notion of a common ancestry.

Observational Studies:

Experiments (e.g., Kwang Jeon’s amoeba study) demonstrate that cells can develop dependency on engulfed bacteria, highlighting the feasibility of endosymbiotic relationships.

Comparing Prokaryotic and Eukaryotic Cells

Feature

Prokaryotes

Nucleus

No (nucleoid region present)

Size

Generally smaller (0.1-5.0 µm)

Membrane-bound organelles

No

DNA Structure

Circular

Ribosomes

Smaller

Reproduction

Binary fission

Examples

Bacteria and Archaea

Key Questions to Answer

What are the membrane-bound structures of the eukaryotic cell?

Include nucleus, mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, lysosomes, and vesicles.

What are the components of the endomembrane system?

Endoplasmic reticulum (rough and smooth), Golgi apparatus, lysosomes, and vesicles.

What is the role of the endomembrane system?

Facilitates the synthesis, modification, transport, and detoxification of cellular materials.

What are the similarities and differences of prokaryotic and eukaryotic cells?

Both have plasma membranes, cytoplasm, and ribosomes. Differences include the presence of a nucleus and membrane-bound organelles in eukaryotes.

What evidence supports the Endosymbiotic Theory?

Presence of circular DNA and ribosomes in mitochondria and chloroplasts, independent reproduction, and genetic similarities with prokaryotic cells.

Summary

Understanding the structures and functions of eukaryotic cells and the evolutionary implications of the endosymbiotic theory highlights the complexity of life. The compartmentalization provided by membrane-bound organelles enhances cellular efficiency, allowing for specialized functions that are essential for survival. This knowledge underscores the significance of both scientific inquiry and personal belief in our understanding of life's origins and development.